Converting an IP address to a number:

Question

Question: When I convert the IP address 192.168.115.67 to a number, is it done like this:
192*256³ + 168*256²+115*256¹+67*256⁰ = 3232265027

or like this:
192*256⁰ + 168*256¹+115*256²+67*256³ = 1131653312

I find both variants online, and frankly it doesn't matter as long as I do all the internal IP-range comparison using the same conversion process variant. But I want to calculate the IP V6 from the IPv4 address, and it seems both variants are on the web... resulting in different IPv6 addresses, and only one can be correct...

I use the 1131653312 variant, as 1131653312 is the variant I saw .NET giving me, but 3232265027 is the variant I used when I did it in C++, and that is also the variant I find on the web for IPv4 to IPv6 conversion, and which I used before I saw that .NET uses variant 1131653312 ...

score 5 · Answer 1 · edited Jun 08 '18 at 15:42

5

It is definitely first one. You can ping and see how ping utility convert it to a.b.c.d notation. If you going to do this conversion I recommend expression: (a << 24) | (b << 16) | (c << 8) | d

edited Jun 08 '18 at 15:42

Zoe

27,060
21
118
148

answered May 28 '10 at 10:57

Andrey

59,039
12
119
163

You can't really say that; it depends on the endianness of his platform. OK, well I suppose you can, as .NET isn't exactly ported to a whole lot of different platforms. But in principle, you can't really say that. – T.E.D. May 28 '10 at 11:00
@T.E.D. as a number it will look like 3232265027. Second question is how it is stored in the memory, and that point i didn't mention at all. – Andrey May 28 '10 at 11:12
Nice, the ping utility confirms it. Didn't know it worked with a plain number. – Stefan Steiger May 28 '10 at 20:03

score 4 · Accepted Answer · edited Jun 08 '18 at 15:42

4

The method resulting in 3232265027 should be correct, as the first number is stored in the highest bits of the IPv4 compatibility part of IPv6:

0000:0000:0000:0000:0000:ffff:AABB:CCDD

where

AA = 192
BB = 168
CC = 0
DD = 1

etc.

https://wikipedia.org/wiki/IPv6

Also, you can't have a 256 in an IP address. The values are 0 - 255 each.

edited Jun 08 '18 at 15:42

Zoe

27,060
21
118
148

answered May 28 '10 at 10:59

Delan Azabani

79,602
28
170
210

score 0 · Answer 3 · answered May 28 '10 at 10:56

0

Numbers are sent in big-endian order over the wire, which is the same as the way they are written (192 is the most significant byte). Thus the first number is the "correct" one. The other variant is how the same bytes will be interpreted on a little-endian architecture, hence the .Net behaviour.

Having said all that, I'm really not sure what the question is, so I can only hope that this exposition constitutes an answer of sorts.

answered May 28 '10 at 10:56

Marcelo Cantos

181,030
38
327
365

The question is, how does the (correct) IP v6 look for the given IP v4. – Stefan Steiger May 28 '10 at 11:39

score 0 · Answer 4 · edited Jun 08 '18 at 15:42

0

The difference has to do with endianness. You are storing it in an integer, but different processors have different byte orderings for their integers (big or little end first). However, that number has to go out over the line, so IP has a specific order it needs the bytes transferred in. That order looks different to bigendian and littleendian machines.

edited Jun 08 '18 at 15:42

Zoe

27,060
21
118
148

answered May 28 '10 at 10:58

T.E.D.

44,016
10
73
134

I don't know much about .net cross different hardware, however isn't .net suposed to abstract byte shifting for integers? – oxygen Jun 09 '12 at 01:12

Converting an IP address to a number:

4 Answers4